Vessel MAWP 720 psi

[johngladstone]

Dears ,

I get vessel it's MAWP is 720 psi @80 F
If I select flange class 300 my question :-
is Design pressure of pipe connect is 740 psi ??

Or you advice use # 400 for more safe and use pipe design pressure 990 to implement ASME B 31.3 to determine the thickness ??
Any input with example or text will be highly appressiate

Thank you
John

 

[mk3223]

As MAWP at 720psi, the CL300 piping is adequate for the vessel, and no need for CL400 piping.
As for the piping, the DP may be determined per the Process requirement, as long as it's =< 740 psig @80F.

 

[johngladstone]

Thank u mk

It mean I can use DP for pipe 740 same as flange class without any problem to implement ASME equation ?

Is MAWP cover whole allowable and non allowable over pressure ?

If MAWP recalculate and I discover it reach
738 psi also can I use cl300 or move into CL400 ?

Best regards
John

 

[LittleInch]

John.

MAWP for a vessel is stamped on a plate and doesn't change. There is NO allowance for over pressure in vessel design codes.

What material is your flange? That affects the pressure rating.

I've never seen or heard of class 400 actually being used. If you can find a supplier then maybe it's an option, but otherwise forget it.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[johngladstone]

Hi littlenech

Flange material is Cs

Is there margin safety when MAWP reach number nearby Design pressure of flange
To jump into next flange class ??

After get MAWP from vessel stamp can I use MAWP of ANSI 16.5 to use in ASME B 31.3 ??

Best regards
John

 

[LittleInch]

John,

Vessel MAWP is the max pressure. There is no operating allowance over and above this number.

The only allowance above that allowed is for pressure relief valves in operation, but you set the pressure relief at or below the MAWP.

Usually you can use the MAWP @the stated temperature as the same number in ASME B16.5 and use it as the design pressure in B31.3

CS doesn't mean anything - you need to know the material specifically - I assume you mean A105, which is good for 720 psi @80F

720 to 740 is tight, but no reason to go to class 600 if you don't have to.

Like I said, I've seen a class 400 flange once in 30 years of this work. Forget they exist, everyone else does.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[johngladstone]

Thank you littlenech for your clarification


I get confuse in one point .
Based on your experience
Margin safety to jump into another flange class
Example
730- 735 MAWP of pressure vessel below flange class pressure 300
Can I jump into another flange class 600 ?
From safety oint of view ?

Best regards
John

 

[LittleInch]

You can, but there is no requirement.

Whilst there is no allowance for overpressure in pressure vessel design, there is in piping design to b 31.3.

You need to set your alarms and safety systems in the pressie vessel at or below the MAWP.

So yes it's close but so what?


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[johngladstone]

It mean I can go into cl 300 even there is difference 1 psi between flange class and MAWP ?
Without any side effect may occur ?

 

[LittleInch]

Yes.

Think off this like a speed limit.

Drive 1mph over the limit and you get a ticket.
At or 1mph under the limit and you don't.

Now how accurate your process control will be at 739 psi is open to question, but in design terms yes you can.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[johngladstone]

Thank you littlenech

Is there any source discuss these situations as examples can refer to it ??

Best regards
John

 

[LittleInch]

You're reading it!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.